My new to me e300d is charging the battery at 14.6 V with no accessories on and warm engine. Is this too high, meaning I need to put in a new voltage regulator?
I haven't checked my 90 300d to see what it runs at. The battery in it was a Walmart cheap battery that is only 2 years old and reading a little over 50 % of the CCA of what it is supposed to be. Also noticing a little rust in the area around the battery (possibly from batteries being overcharged?)
Thanks!

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1990 300d 2.5 turbo
1995 E300d

It's on the high end but wouldn't worry about it.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Ok, I'll leave it for now.

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1990 300d 2.5 turbo
1995 E300d

I ended up ordering a new beru voltage regulator. It was only 21$ so I figured it was worth a try. If the new one still charges at 14.6 or 14.7, I'll have a spare. It might be a battery issue too. The one I have in there now is smaller than it's supposed to be (out of my TDI), because the one it came with tested low, and my spare TDi one tested better. I did check resistance between alternator body and ground terminal, and almost no resistance.

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1990 300d 2.5 turbo
1995 E300d

This post has comments about AGM batteries that I would suggest you use for any starting/cranking issues:

95 E300D question about AGM battery

Well, I would be really happy if mine charges at 14.6 volts.

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84 300D, 82 Volvo 244Gl Diesel

I haven't had good experiences with the couple AGM batteries I have worked with. I have never bought one myself, but I bought a car with one in it that was a couple years old, and only produced about 60% of rated CCA. Also had a friend that paid 300$ for an optima, to find it was bad 2 months later. It was replaced with a good one for free, but still. My regular batteries last 7 years or so. My plan is to not drive this car too much in this winter, so reduce exposure to salt...so am not replacing battery or voltage regulator yet. The new one I received says 14.5 volts, so I guess the old one is not far off. Good to have a spare in the car just in case, I suppose.

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1990 300d 2.5 turbo
1995 E300d

I doubt if I would ever go back to the old style lead acid battery after having an AGM to start my 95 E300D. Significant difference in cranking rpm and starts even with a couple of open glow plugs.

What brand AGM battery are you using? I like the idea of going with what is working well for others. I have had good luck with NAPA conventional batteries.

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1990 300d 2.5 turbo
1995 E300d

I'd be hesitant to put an AGM battery in a vehicle that wasn't designed for one. Im not experienced in this mod but would look into before doing it as the flooded battery charging system wasn't designed to charge AGM's. Again I'm not speaking from experience on this, just hesitant and cautious.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Mine is an Interstate AGM from Costco. I prefer to use Costco because they have never questioned a problem battery. Plus their price is great.

I've had no problem with the battery charging, but I do connect my CTEK charger periodically to keep it topped up if not driven for a while.

How did you test the cold cranking amps and was the battery charged before the test?

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84 300D, 82 Volvo 244Gl Diesel

The battery was charged before the test, and it was that way when I got it, I am guessing it sat dead for a while. I have a "Solar" CCA tester. It was in a car that had a leaking injection pump and had been sitting. It was one of those batteries that sucked, but not bad enough to buy a new one, so I limped it along for 3 years or so. With the optima, I seem to remember him going through 2 bad "brand new" batteries before he got a good one. The good one seems to be going fine, since we inherited the car in the spring, the battery does hold a charge. In my experience with renewable energy systems the AGM batteries last about as long as FLA batteries and are much more expensive. The main advantage is for those who would not maintain them (give an equalizing charge, and top off with distilled water). I am open to considering particular brand AGM batteries that have proved to last longer than 7 years.

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1990 300d 2.5 turbo
1995 E300d

An internet search has informed me that AGM batteries need to charge at about 14/15 volts and not higher.

The smart AGM chargers may not start to charge if the battery is less than 10 volts. Many owners think the battery is bad when it is not. Simple solution connect another charged battery in parallel. Then keep checking the ' bad ' one til it's voltage is above 10 volts and finish charging it after disconnecting the parallel battery.

There is a lot of good information about how to maintain AGM battteries. Main benefit, to me, is easier starting of my car.

https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

Added Saturday 12/9/2023

https://www.interstatebatteries.com/blog/what-is-an-agm-battery-and-whats-the-big-deal

How cold is it by you?

The voltage regulator can adjust a bit for temperature.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)